Abstract

For intermediate-band solar cells containing GaAs/InAs quantum dots(QDs), the QD density dependence of the power conversion efficiency (PCE) was theoretically calculated for various sun concentrations under AM1.5 conditions based on detailed balance principles. A QD density of over 5 × 1013 cm−2 was required to achieve a PCE of more than 50% under 10 000 suns. However, under the photo-filled state and 1 sun, the PCE decreased over a wide total QD density range from about 3 × 1010 to 1 × 1013 cm−2. This reduction was attributed to the negative net carrier generation rate through the intermediate band, which was due to insufficient two-step optical absorption. The short-circuit current density increased as the QD density increased up to about 1 × 1011 cm−2 and it then saturated. In contrast, the open-circuit voltage decreased with increasing QD density. This reduction in the open-circuit voltage was suppressed at high sun concentrations.

Received 15 October 2012Accepted 12 November 2012Published online 26 December 2012

Acknowledgments:

This work was supported by the Incorporated Administrative Agency New Energy and the Industrial Technology Development Organization (NEDO) under the Ministry of Economy, Trade and Industry (METI), Japan.